The program objective is to facilitate the management of the NIH animal Genetic Resource (NIHAGR) through the development and utilization of techniques such as collection, culture, freezing and transfer of embryos and gametes for cryobanking genetic material and improving reproductive potential. The NIHAGR maintains a number of critical species and, within species , a vast number of invaluable genotypes used in biomedical research. Embryo preservation uses a cryoprotectant in the freezing medium which allows sufficient dehydration to protect the blastomeres during freezing. Following thawing and dilution of the cryoprotectant, embryos are cultured to assess in vitro development. Transplantation of embryos into recipient females monitors in vitro fertilization and ova freezing are being examined as techniques to salvage limited genetic material from single females or strains with poor in vitro fertilization rates. Banked embryos are maintained in a frozen state until needed for rederivation. A primary focus of laboratory efforts is the study and optimization of cryobanking technology in mice and rabbits and more recently, in rats. A major research finding is that embryo freezability is confounded and influenced markedly by mouse genotype. Such responses have been examined in over 56 genotypes, most of which display genotype-specific survival rates to standardize embryo freeze-thawing procedures. Ancillary projects are oriented toward the comparative aspects of improving long-term embryo storage with particular emphasis on the study of cryoprotectants and enhancing methods for embryo freezing, thawing, dilution and transfer. Efforts in the rabbit focus on improvements in collection procedures and preservation of embryos.